An anode edge coating latex emulsion, a preparation method, an anode ceramic slurry and an anode pole piece

Abstract

The application belongs to the field of new energy materials, and discloses a negative electrode edge coating emulsion, which is obtained by free radical emulsion polymerization reaction of soft monomers, hard monomers and functional monomers as reaction monomers in the presence of an emulsifier and an initiator; the weight of the emulsifier is equal to or less than 0.4 wt% of the total weight of the reaction monomers; and the weight of the functional monomers is equivalent to 5 wt% to 15 wt% of the total weight of the reaction monomers. Compared with traditional emulsions, the negative electrode edge coating emulsion has a higher surface tension, and can match the negative electrode slurry with a high surface tension after the ceramic slurry is prepared in proportion, so as to realize the purpose of no material leakage and no mutual penetration between the two, and excellent lap performance; meanwhile, the edge coating can provide good peeling force, and realize good adhesion between the edge coating and the separator; meanwhile, the application also discloses the use of the negative electrode edge coating emulsion, a negative electrode ceramic slurry and a negative electrode sheet.

Description

Technical Field

[0001] This invention relates to the field of new energy materials, specifically to a negative electrode edge-coated emulsion, a preparation method, a negative electrode ceramic slurry, and a negative electrode sheet. Background Technology

[0002] With the increasing demand for lithium-ion batteries, people are paying more and more attention to their safety. During repeated cycles, lithium crystals can form in lithium-ion batteries, which may puncture the separator. This can lead to problems ranging from large voltage differences to short circuits. Therefore, it is necessary to introduce edge coating adhesive into the battery manufacturing coating process.

[0003] Traditional electrode fabrication processes lack edge coating adhesive, involving direct cutting on copper foil, which can lead to misalignment or damage to the negative electrode material area. By introducing an edge coating adhesive blended with boehmite to create a negative electrode ceramic slurry, which is then coated onto the sides of the electrode, the equipment can automatically identify and cut during the cutting process. For a more vivid demonstration of the edge coating adhesive's function, please refer to the attached diagram. Figure 37 and appendix Figure 1 To be continued Figure 36 , attached Figure 37 In the diagram, the electrode sheet is labeled 1, the negative electrode slurry layer (black during production) is labeled 2, and the negative electrode ceramic slurry (white during production) is labeled 3. (The remaining text appears to be unrelated and possibly machine-generated.) Figure 32 The arrangement relationship between the negative electrode slurry layer and the negative electrode ceramic slurry is displayed. Automated cutting can be performed by visually identifying the intersection of the two. Correspondingly, in the attached... Figures 1 to 36 In the image, the background is the copper electrode sheet, the white paste is the negative electrode ceramic paste, and the black paste is the negative electrode paste layer.

[0004] In the above application scenarios, the negative electrode slurry has a high surface tension, and such negative electrode slurry requires a matching edge coating agent with a high surface tension. If an edge coating agent with a low surface tension is used, the negative electrode ceramic slurry will move towards the negative electrode slurry. This phenomenon is known as the Marangoni effect.

[0005] Preliminary experiments revealed an inverse relationship between the increase in surface tension and peel force, indicating a contradiction between the surface tension and peel force of the edge-coated adhesive. Peel force is a crucial performance indicator for achieving adhesion between the edge-coated adhesive and the diaphragm, and a higher surface tension in the edge-coated adhesive is essential to ensure that the negative electrode ceramic slurry does not negatively impact the performance of the main material. In most of the earlier experiments, it was impossible to guarantee a uniform improvement in both properties. Summary of the Invention

[0006] The purpose of this invention is to provide a negative electrode edge-coated emulsion, which has a higher surface tension than traditional emulsions. After preparing ceramic slurry according to the specified ratio, it can be matched with the high surface tension negative electrode slurry to achieve the purpose of preventing material flow and interpenetration between the two, and has excellent bonding performance. At the same time, the edge coating can provide good peel force and achieve good adhesion with the separator.

[0007] Meanwhile, the present invention also discloses the preparation method of the negative electrode edge-coated emulsion, the negative electrode ceramic slurry, and the negative electrode sheet.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A negative electrode edge-coated emulsion, wherein the negative electrode edge-coated emulsion is obtained by free radical emulsion polymerization in the presence of a soft monomer, a hard monomer, and a functional monomer as reactive monomers, under the condition of an emulsifier and an initiator;

[0010] The weight of the emulsifier is equal to or less than 0.4 wt% of the total weight of the reactive monomers;

[0011] The weight of the functional monomer is equivalent to 5 wt% to 15 wt% of the total weight of the reactive monomer;

[0012] The weight of the soft monomer is equivalent to 52 wt% to 72 wt% of the total weight of the reactive monomers;

[0013] The weight of the hard monomer is equivalent to 18 wt% to 36 wt% of the total weight of the reactive monomers;

[0014] The functional monomer contains at least one functional group selected from carboxyl, hydroxyl, and amide groups;

[0015] In this invention, some functional monomers are hard monomers or soft monomers. Unless otherwise specified, the hard monomers and soft monomers mentioned above do not contain functional monomers. Generally, hard monomers and soft monomers are preferably acrylate / methacrylate monomers, but other non-ester monomers such as styrene, acrylonitrile and other oil-soluble monomers containing olefin bonds may also be included.

[0016] In some embodiments of the present invention, the functional monomer is more preferably 10wt% to 15wt% or 5wt% to 10wt%.

[0017] This invention improves the surface tension of traditional edge-coating emulsions from 32 mN / m to about 40 mN / m through the following two core methods, so as to adapt to the surface tension of the negative electrode slurry while maintaining excellent peel strength.

[0018] 1. Reduce the amount of emulsifier. Studies have found that the less surfactant used, the greater the surface tension. At the same time, reducing the amount of surfactant will increase the instability of the emulsion, thereby reducing the peel force of the edge coating.

[0019] 2. To address the weakening of the peel strength of the edge coating due to the reduction in emulsifier dosage, a certain amount of functional monomers is used to improve this weakening trend.

[0020] Functional monomers contain amino, carboxyl, hydroxyl, and amide groups, which are polar groups. They increase the intermolecular interaction forces at the adhesive interface, improve interfacial adhesion conditions, and thus enhance interfacial adhesion. They also change the mechanical and rheological properties of the adhesive layer, such as increasing cohesive strength and elastic modulus, and raising the glass transition temperature and bulk viscosity. Therefore, under the premise of controlling the amount of surfactant, using functional monomers is an effective means to improve the problem of weakened peel force caused by the reduction of surfactant.

[0021] Meanwhile, during the verification process of adjusting the dosage of functional monomers, it was further discovered that increasing the dosage of functional monomers leads to a slight increase in surface tension. Although the effect on surface tension is not as significant as that of emulsifiers, the appropriate dosage of functional monomers can effectively improve surface tension, although the mechanism is not yet clear.

[0022] In this invention, most of the functional monomers are water-soluble monomers, and a small portion are oil-soluble monomers.

[0023] In summary, this invention increases surface tension by reducing the amount of emulsifier and overcomes the weakening of peel force caused by the reduction in emulsifier dosage by using functional monomers. Ultimately, the negative electrode edge coating emulsion of this invention exhibits improved surface tension and good peel force when applied to negative electrode ceramic slurry.

[0024] In the above-mentioned negative electrode edge coating emulsion, the soft monomer is one or more of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, isooctyl acrylate, and lauryl acrylate.

[0025] The hard monomer is one or more of ethyl methacrylate, vinyl acetate, methyl methacrylate, styrene, and acrylonitrile;

[0026] The functional monomer is one or more of acrylic acid, acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N,N-dimethylacrylamide.

[0027] Regarding soft monomers and hard monomers, there is no strict definition in this field of the dividing point of glass transition temperature for linear polymers. Generally speaking, monomers with higher glass transition temperatures are hard monomers, and monomers with lower glass transition temperatures are soft monomers. Here, glass transition temperature generally refers to the glass transition temperature of simple linear polymers. Soft monomers are used in the coating field to provide adhesion, while hard monomers provide adhesive force. In this invention, excessive soft monomers cause edge coating peeling and stringing, while excessive hard monomers cause the coating to become too hard. Excess of either type of monomer will lead to impaired peel force.

[0028] Preferably, the polymer content in the negative electrode edge coating emulsion is 20wt% to 24wt%; preferably, the weight ratio of the soft monomer to the hard monomer is 6:4 to 7:3.

[0029] In the aforementioned negative electrode edge-coating emulsion, the polymer is either a linear polymer or a crosslinked polymer. If it is a linear polymer, no crosslinking monomer is required; if it is a crosslinked polymer, a crosslinking monomer is required. The amount of crosslinking monomer in the polymer is equivalent to 0-0.4 wt% of the total monomer weight. Commonly used crosslinking agents in the art are applicable in this invention, generally compounds with multiple double bonds, such as N,N-methylenebisacrylamide, divinylbenzene, dipropylene glycol diacrylate, etc.

[0030] In the above-mentioned negative electrode edge coating emulsion, the emulsifier is one or more combinations of anionic surfactants and nonionic surfactants;

[0031] The anionic surfactant is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, and esterified polyoxyethylene alkyl ether.

[0032] The nonionic surfactant is one or more combinations of dodecylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and condensates of alkylphenol and ethylene oxide.

[0033] The emulsifier is present in an amount equivalent to 0.25 to 0.4 wt% of the total weight of the reactants.

[0034] Generally, when most emulsifiers are controlled at 0.25wt% or higher, the stability of the emulsion system can be guaranteed. If the concentration is lower than this value, only a portion of the emulsifiers can maintain the stability of the emulsion, and most of the system is at risk of demulsification.

[0035] During the experiment, a high-performance emulsifier was screened out. The emulsifier is sodium dodecyl sulfate, and the weight of the emulsifier can be equivalent to 0.1 to 0.4 wt% of the total weight of the reactants.

[0036] Meanwhile, the present invention also discloses a method for preparing the above-mentioned negative electrode edge-coated emulsion, wherein the negative electrode edge-coated emulsion is obtained by free radical emulsion polymerization.

[0037] The method for free radical emulsion polymerization is as follows:

[0038] Step 1: Weigh water, part of the emulsifier and part of the reactant monomer into a flask, stir, purge with nitrogen and heat to 75-80°C. After the temperature stabilizes, start adding the initiator solution dropwise.

[0039] Step 2: Add the remaining emulsifier and remaining reactive monomers to water and stir to obtain a homogeneous pre-emulsion;

[0040] Step 3: After the reaction stabilizes, begin adding the pre-emulsion and the remaining initiator dropwise;

[0041] Step 4: After the addition is complete, keep the reaction at a certain temperature for a period of time, raise the temperature to 80-90℃, and add the initiator again to eliminate residue;

[0042] Step 5: Neutralize the product with alkali to adjust the pH, then filter to obtain the edge-coated latex;

[0043] The reactive monomers include soft monomers, hard monomers, and functional monomers;

[0044] The weight of the emulsifier is equal to or less than 0.4 wt% of the total weight of the reactive monomers;

[0045] The weight of the functional monomer is equivalent to 5 wt% to 15 wt% of the total weight of the reactive monomer;

[0046] The weight of the soft monomer is equivalent to 52 wt% to 72 wt% of the total weight of the reactive monomers;

[0047] The weight of the hard monomer is equivalent to 18 wt% to 36 wt% of the total weight of the reactants;

[0048] The functional monomer contains at least one functional group selected from carboxyl, hydroxyl, and amide groups.

[0049] The monomer distribution ratio in steps 1 and 2 is 0.5:2.5 to 1:1; the initiator distribution ratio in steps 1 and 3 is 1:1 to 1:2.5; the emulsifier ratio in steps 1 and 2 is 0.5:2.5 to 1:1; a water-soluble initiator is selected, and its amount is controlled at 0.3% to 1% of the total weight of the reacting monomers; the dropping time in step 3 is 1 to 2 hours; the pre-emulsion and the remaining initiator are added dropwise 0.5 to 1.5 hours after the reaction stabilizes in step 3.

[0050] In addition, the present invention also discloses a negative electrode ceramic slurry, comprising the negative electrode edge coating emulsion and boehmite as described above; the solid content of the negative electrode ceramic slurry is 35-45 wt%.

[0051] Finally, the present invention also discloses a negative electrode sheet, comprising a current collector, a negative electrode slurry coated on the center of one side surface of the current collector, and a negative electrode ceramic slurry as described above coated on the edge of one side surface of the current collector; there is an interface between the negative electrode slurry and the negative electrode ceramic slurry.

[0052] In embodiments of the present invention, relevant verifications were conducted using a negative electrode slurry with a surface tension of 40±2mN / m and the negative electrode ceramic slurry of the present invention. When the surface tension difference between the two is small, good interface clarity can be maintained. In several cases of the present invention, it is verified that the surface tension difference between the negative electrode ceramic slurry and the negative electrode slurry should not be greater than 6mN / m. More specifically, when the surface tension is lower than that of the negative electrode slurry, the difference should not be greater than 4mN / m, and when the surface tension is higher than that of the negative electrode slurry, the difference should not be greater than 6mN / m.

[0053] Compared with the prior art, the beneficial effects of the present invention are:

[0054] 1. This invention uses a suitable ratio of soft and hard monomers to ensure basic peel performance and the softness or hardness of the adhesive;

[0055] 2. By reducing the amount of surfactant, the surface tension is increased to make the interface between the negative electrode ceramic slurry and the negative electrode slurry more clearly defined;

[0056] 3. By using a certain amount of functional monomers, the trend of decreased peel strength caused by reduced surfactant dosage was reversed. Simultaneously, increasing the amount of functional monomers leads to an increase in surface tension. While its impact on surface tension is not as significant as that of surfactants, the appropriate use of functional monomers can effectively improve surface tension.

[0057] Through the above optimizations, the negative electrode edge-coating emulsion of the present invention, after being prepared into a negative electrode ceramic slurry, can maintain a clear interface with the negative electrode slurry, without problems such as cross-contamination, which is conducive to machine vision recognition for automated cutting, while ensuring the basic mechanical properties of the negative electrode ceramic slurry, such as peel strength. Attached Figure Description

[0058] Figure 1 Photographs showing the overlap between the emulsion prepared in Example 1 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry;

[0059] Figure 2 Photographs showing the overlap between the emulsion prepared in Example 2 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry;

[0060] Figure 3 Photographs showing the overlap between the emulsion prepared in Example 3 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0061] Figure 4 Photographs showing the overlap between the emulsion prepared in Example 4 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0062] Figure 5 Photographs showing the overlap between the emulsion prepared in Example 5 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0063] Figure 6 Photographs showing the overlap between the emulsion prepared in Example 6 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0064] Figure 7 Photographs showing the overlap between the emulsion prepared in Example 7 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0065] Figure 8 Photographs showing the overlap between the emulsion prepared in Example 8 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0066] Figure 9 Photographs showing the overlap between the emulsion prepared in Example 9 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry;

[0067] Figure 10 Photographs showing the overlap between the emulsion prepared in Example 10 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0068] Figure 11 Photographs showing the overlap between the emulsion prepared in Example 11 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0069] Figure 12 Photographs showing the overlap between the emulsion prepared in Example 12 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry;

[0070] Figure 13 Photographs showing the overlap between the emulsion prepared in Example 13 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0071] Figure 14 This is a photograph showing the overlap between the emulsion prepared in Example 14 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0072] Figure 15 Photographs showing the overlap between the emulsion prepared in Example 15 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0073] Figure 16 Photographs showing the overlap between the emulsion prepared in Example 16 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0074] Figure 17 Photographs showing the overlap between the emulsion prepared in Example 17 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0075] Figure 18 Photographs showing the overlap between the emulsion prepared in Example 18 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0076] Figure 19 Photographs showing the overlap between the emulsion prepared in Example 19 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0077] Figure 20 Photographs showing the overlap between the emulsion prepared in Example 20 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0078] Figure 21 Photographs showing the overlap between the emulsion prepared in Example 21 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry;

[0079] Figure 22 Photographs showing the overlap between the emulsion prepared in Example 22 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry;

[0080] Figure 23 Photographs showing the overlap between the emulsion prepared in Example 23 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0081] Figure 24 This is a photograph showing the overlap between the emulsion prepared in Example 24 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0082] Figure 24 This is a photograph showing the overlap between the emulsion prepared in Example 24 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0083] Figure 25 Photographs showing the overlap between the emulsion prepared in Example 25 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0084] Figure 26 Photographs showing the overlap between the emulsion prepared in Example 26 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0085] Figure 27 Photograph of the overlap between the emulsion prepared in Example 27 and the negative electrode slurry after it was made into a negative electrode ceramic slurry;

[0086] Figure 28 Photographs showing the overlap between the emulsion prepared in Example 28 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0087] Figure 29Photographs showing the overlap between the emulsion prepared in Example 29 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0088] Figure 30 Photographs showing the overlap between the emulsion prepared in Example 30 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0089] Figure 31 Photographs showing the overlap between the emulsion prepared in Example 31 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0090] Figure 32 Photographs showing the overlap between the emulsion prepared in Example 32 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0091] Figure 33 Photographs showing the overlap between the emulsion prepared in Example 33 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0092] Figure 34 Photograph of the overlap between the emulsion prepared in Example 34 and the negative electrode slurry after it was made into a negative electrode ceramic slurry;

[0093] Figure 35 Photographs showing the overlap between the emulsion prepared in Example 35 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0094] Figure 36 Photographs showing the overlap between the emulsion prepared in Example 36 and the negative electrode slurry after it has been prepared into a negative electrode ceramic slurry;

[0095] Figure 37 This is a schematic diagram of the negative electrode ceramic slurry and the negative electrode slurry layer in the background art. Detailed Implementation

[0096] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0097] Part One explores the effects of emulsifier ratio and functional monomers on peel strength, surface tension, and overlap.

[0098] The preparation method of the negative electrode edge-coated emulsion of the present invention is as follows:

[0099] Step 1: Weigh deionized water, part of the emulsifier and part of the monomer into a flask, stir, pass nitrogen through and heat to 75-80℃. After the temperature stabilizes, start adding the initiator solution dropwise.

[0100] Step 2: Add the remaining emulsifier and monomer to deionized water and stir thoroughly to obtain a uniform pre-emulsion;

[0101] Step 3: After the reaction has stabilized for 1 hour, start adding the pre-emulsion and the remaining initiator dropwise, and complete the addition within 1.5 hours;

[0102] Step 4: After the addition is complete, keep the reaction at this temperature for 2 hours, then raise the temperature to 85°C and add 0.1% of the total monomer mass of the initiator again to eliminate residue; stop the reaction after 2 hours of residue elimination.

[0103] Step 5: Neutralize the product with sodium hydroxide to adjust the pH, then filter to obtain the edge coating emulsion.

[0104] The types of emulsifiers and monomers used in the above methods are shown in Table 1 below;

[0105] In Examples 1 to 4, the weight of deionized water was 315g; the weight of all monomers was 100g; the initiator was ammonium persulfate, and the weight of the initiator was 1g, with a distribution ratio of 1:2.5 in steps 1 and 3; the distribution ratio of emulsifier 1 in step 2 was 0.5:2.5; and the distribution ratio of monomers in steps 1 and 2 was 0.5:2.5.

[0106] In Examples 5 to 9, the weight of deionized water was 350g; the weight of all monomers was 100g; the initiator was ammonium persulfate, and the weight of the initiator was 0.5g, with a distribution ratio of 1:1 in steps 1 and 3; the distribution ratio of emulsifier 1 and the emulsifier in step 2 was 1:2; and the distribution ratio of monomers in steps 1 and 2 was 1:2.

[0107] In Examples 10 to 14, the weight of deionized water was 400g; the weight of all monomers was 100g; the initiator was ammonium persulfate, and the weight of the initiator was 0.3g, with a distribution ratio of 1:1.5 in steps 1 and 3; the distribution ratio of emulsifier 1 and the emulsifier in step 2 was 1:1; and the distribution ratio of monomers in steps 1 and 2 was 1:1.

[0108] In Table 1 below, the weight ratio of SR-10 to OP10 in the compound emulsifier SR-10 / OP10 is 2:1; emulsifier OP-10: condensate of alkylphenol and ethylene oxide; SR-10: esterified polyoxyethylene alkyl ether.

[0109] Table 1 Formula Table (Unit: g)

[0110]

[0111]

[0112] Part Two explores the effects of soft and hard monomers on peel force, surface tension, and overlap.

[0113] The preparation method is the same as in Part 1. In this part, the functional monomers are acrylamide and acrylic acid, and the total amount of the two is 10 wt% of the total monomers. In this part, the parameters such as the proportion of functional monomers, the type and amount of initiator, and the amount of water are the same as in Example 8. The types and amounts of soft monomers and hard monomers are changed in this part, and can be found in Table 2.

[0114] Table 2 Formula Table Unit: g

[0115]

[0116]

[0117] Part Three explores the influence of the ratio of soft to hard monomers on peel force, surface tension, and overlap.

[0118] The process in this section is the same as in the first section, and the formulation is largely the same as in Example 8, except that the ratio of butyl acrylate to methyl methacrylate is different. Refer to Table 3 for the formulation; the total amount of butyl acrylate and methyl methacrylate is 90 wt% of the total monomers.

[0119] Table 3 Formula Table Unit: g

[0120]

[0121] Part Four explores the effects of the proportion of functional monomers on peel force, surface tension, and overlap. The process in this part is the same as in Part One; the amount and type of emulsifier and water remain unchanged; the remaining variables are detailed in Table 4 below.

[0122] Table 4 Formula Table (Unit: g)

[0123]

[0124] Part 5 explores the effect of the ratio of crosslinking monomers on peel force, surface tension, and overlap. The process in this part is the same as in Part 1, and the formulation is largely the same as in Example 8. The difference is that this part adds crosslinking monomers based on Example 6. The specific selection of the type and amount of crosslinking monomers (equivalent to the percentage of the total weight of soft monomers, hard monomers, and functional monomers) is shown in Table 5 below.

[0125] Table 5 Formula Table (Unit: g)

[0126]

[0127] Performance testing

[0128] The preparation method and peel strength performance test of the negative electrode ceramic slurry are as follows:

[0129] The negative electrode edge coating emulsion is mixed with boehmite to form a negative electrode ceramic slurry with a solid content of 45 wt%; the solid content mentioned here refers to the content of boehmite, polymer and other substances.

[0130] The negative electrode ceramic slurry was coated onto copper foil and baked in an oven at 110°C for 20 minutes. It was then hot-pressed with a diaphragm at 100°C and 2MPa for 1 minute, and the peel strength was tested.

[0131] The negative electrode slurry (surface tension approximately 40±2 mN / m) and the negative electrode ceramic slurry are overlapped according to the following method:

[0132] A drop of the negative electrode slurry the size of a one-yuan coin was placed in the water. A drop of the same size of negative electrode ceramic slurry was then placed 0.5 cm from the edge of the negative electrode slurry. The two slurries were allowed to touch at their edges for 3 minutes. The boundary shift and spreading issues were observed upon contact. The presence of either issue indicated cross-contamination; the absence of any issue indicated excellent bonding performance. The bonding performance between the negative electrode slurry and the negative electrode ceramic slurry was observed. The test results from Parts 1 to 5 are shown in Table 6 below.

[0133] Table 6 Test Results

[0134]

[0135]

[0136] Results analysis:

[0137] 1. Referring to Examples 1 to 4, Examples 5 to 9, and Examples 10 to 14, it can be seen that the amount of emulsifier is the core factor affecting surface tension; when the amount of emulsifier is less than 0.4%, the surface tension is greater than 38 mN / m; in a few cases, when the amount of emulsifier reaches 0.5%, a large surface tension can still be maintained, such as in Example 11.

[0138] Its effectiveness in preventing seepage and cross-contamination is evident. Figures 1 to 14 ,from Figures 1 to 14 The results show that as the amount of emulsifier decreases, the interface becomes clearer; at the same time, as can be seen from the above examples, the peeling force decreases significantly as the amount of emulsifier decreases.

[0139] 2. As can be seen from Examples 15 to 19, by using appropriate proportions of soft and hard monomers, various optional soft and hard monomers can achieve generally good peeling force and surface tension when properly mixed.

[0140] pass Figures 15 to 19 It is evident that the interfaces of each sample are very clear, demonstrating excellent effectiveness in preventing penetration and cross-contamination.

[0141] 3. As can be seen from Examples 20 to 24 and Example 8, the ratio of soft to hard monomers has a significant impact on peel strength, but little impact on surface tension, which can generally be maintained above 39 mN / m. In this invention, soft monomers provide adhesion, and hard monomers provide bonding strength. Excessive soft monomers lead to stringing during edge coating peeling, while excessive hard monomers result in overly hard coating. An excess of either monomer will impair peel strength.

[0142] pass Figures 20 to 24 It is evident that the interfaces of each sample are very clear, demonstrating excellent effectiveness in preventing penetration and cross-contamination.

[0143] 4. As can be seen from Examples 25 to 30 and Example 8, when the weight ratio of soft monomer to hard monomer is fixed, when the amount of functional monomer is reduced to 0, the peel force and surface tension are significantly reduced. When the amount of functional monomer is increased to 2.5 wt%, the surface tension is significantly improved and the interface is clear, but the improvement in peel force is still not obvious. When the amount of functional monomer is increased to 5 wt%, the peel force is improved to a certain extent, reaching 0.199 N / cm.

[0144] exist Figures 25 to 33 middle, Figure 25 The obvious blurring of the interface further proves that the reduction in surface tension is the core reason for penetration and material cross-contamination.

[0145] In this invention, the functional monomers have the following functions: 1. They compensate for the decrease in peel strength caused by the reduction of emulsifier; 2. There is a correlation between the presence or absence of functional monomers and the surface tension. Changes in the amount of functional monomers have a significant impact on surface tension, but the impact is not enough to affect the clarity of the interface. As seen in Examples 25 to 30, when the amount of functional monomers changes from 0 to 20, the peel strength undergoes a process of increase and decrease, with the optimal amount of functional monomers for peel strength being 10%. As seen in Examples 27, 31, and 32, the choice of functional monomer type has a relatively significant impact on peel strength. From Examples 25 to 30, the amount of functional monomers has little impact on the clarity of the interface.

[0146] 5. As can be seen from Examples 34 to 36, the use of crosslinking monomers can further improve the peeling force, without affecting the surface tension. The interface clarity of each sample is very good, and it has excellent effects in preventing penetration and cross-contamination.

[0147] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A negative electrode edge-coated emulsion, characterized in that, The negative electrode edge-coated emulsion is obtained by free radical emulsion polymerization in the presence of emulsifiers and initiators, using soft monomers, hard monomers, and functional monomers as reactive monomers. The weight of the emulsifier is equal to or less than 0.4 wt% of the total weight of the reactive monomers; The weight of the functional monomer is equivalent to 5 wt% to 15 wt% of the total weight of the reactive monomer; The weight of the soft monomer is equivalent to 52 wt% to 72 wt% of the total weight of the reactive monomers; The weight of the hard monomer is equivalent to 18 wt% to 36 wt% of the total weight of the reactive monomers; The functional monomer contains at least one functional group selected from carboxyl, hydroxyl, and amide groups.

2. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The soft monomer is one or more of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, isooctyl acrylate, and lauryl acrylate. The hard monomer is one or more of ethyl methacrylate, vinyl acetate, methyl methacrylate, styrene, and acrylonitrile; The functional monomer is one or more of acrylic acid, acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N,N-dimethylacrylamide.

3. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The polymer content in the negative electrode edge coating emulsion is 20wt% to 24wt%. The weight ratio of the soft monomer to the hard monomer is 6:4 to 7:

3.

4. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The polymer in the negative electrode edge coating emulsion is a linear polymer or a cross-linked polymer; The monomers used to prepare the polymer also include crosslinking monomers, and the amount of crosslinking monomers used is equivalent to 0 to 0.4 wt% of the total weight of the soft monomers, hard monomers, functional monomers and crosslinking monomers. The emulsifier is one or a combination of two of anionic surfactants and nonionic surfactants; The anionic surfactant is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, and esterified polyoxyethylene alkyl ether. The nonionic surfactant is one or more combinations of dodecylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and condensates of alkylphenol and ethylene oxide. The emulsifier is present in an amount equivalent to 0.25 wt% to 0.4 wt% of the total weight of the reactants.

5. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The emulsifier is sodium dodecyl sulfate, and the weight of the emulsifier is equivalent to 0.1 wt% to 0.4 wt% of the total weight of the reactants.

6. A method for preparing a negative electrode edge-coated emulsion as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Weigh water, part of the emulsifier and part of the reactant monomer into a flask, stir, purge with nitrogen and heat to 75-80°C. After the temperature stabilizes, start adding the initiator solution dropwise. Step 2: Add the remaining emulsifier and remaining reactive monomers to water and stir to obtain a homogeneous pre-emulsion; Step 3: After the reaction stabilizes, begin adding the pre-emulsion and the remaining initiator dropwise; Step 4: After the addition is complete, keep the reaction at a certain temperature for a period of time, raise the temperature to 80-90℃, and add the initiator again to eliminate residue; Step 5: Neutralize the product with alkali to adjust the pH, then filter to obtain the edge-coated emulsion.

7. The method for preparing the negative electrode edge-coated emulsion according to claim 6, characterized in that, The monomer distribution ratio in steps 1 and 2 is 0.5:2.5 to 1:1; the initiator distribution ratio in steps 1 and 3 is 1:1 to 1:2.5; the emulsifier ratio in steps 1 and 2 is 0.5:2.5 to 1:1; a water-soluble initiator is selected, and its amount is controlled at 0.3% to 1% of the total weight of the reacting monomers; the dropping time in step 3 is 1 to 2 hours; the pre-emulsion and the remaining initiator are added dropwise 0.5 to 1.5 hours after the reaction stabilizes in step 3.

8. A negative electrode ceramic slurry, characterized in that, It includes the negative electrode edge coating emulsion as described in any one of claims 1 to 6, and boehmite; the solid content of the negative electrode ceramic slurry is 35wt% to 45wt%.

9. A negative electrode sheet, characterized in that, It includes a current collector, a negative electrode slurry coated on the center of one side surface of the current collector, and a negative electrode ceramic slurry as described in claim 8 coated on the edge of one side surface of the current collector; there is an interface between the negative electrode slurry and the negative electrode ceramic slurry.

10. The negative electrode sheet according to claim 9, characterized in that, The surface tension of the negative electrode slurry is 38–42 mN / m, and the surface tension of the negative electrode ceramic slurry is 38–45 mN / m.

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